Tomahawk, a free, open-source music player that’s still at a fairly early version (0.0.3), takes a big step in this direction. First, it locates the music on all of your computers (i.e. home and work), and connects with your friends’ libraries as well, to create one big library. Then, it lets you build playlists from that music — playlists that can come from MOG, Rdio, Last.fm, Apple.com, YouTube, and a variety of other places.

What is new in 0.0.3

* Show spinner while resolving playlists.
* Go back to previous page visible when deleting a playlist.
* Fixed issue where automatic playlists and station summaries were not
updated in the playlist header.
* Fixed an issue which caused duplicate items when rescanning.
* Revert change introduced in 0.0.2 causing Twitter protocol to not try
to reconnect to a peer if it couldn't connect the first time the plugin
was connected. This caused confusing (and for most unwanted) behavior.
* Fix crashes in Twitter authentication.
* Properly honor the chosen port number if a static host and port are
marked as preferred.
* Don't automatically try to resolve all incoming playback logs. This
speeds up importing sources a lot.
* Faster painting of playlists with lots of unresolved tracks.
* Prefer local results when results' score is equal.
* (Windows) The tomahawk:// protocol handler works on Windows now.
* (Windows) Fixed launching Tomahawk from Windows installer with admin privileges.
* (Windows) Prevent launching a second instance on Windows.